5V 4 RELAY BOARD -
All 4 relays are individually driven by OPTO ISOLATOR chips.
Power supply -
LED Indicators for Relay ON .
LOGIC LOW Relay ON .
Relay Contacts NO, NC, COMMON extended using individual screw terminals.
Relay coils back EMF protected with diodes.
Always make GND common while using with boards like Arduino.
Seperate power source required for Realay board.Do not power it from Arduino.